The present invention relates to an apparatus for use in a vehicle suspension and, more particularly, to an apparatus for use in helping to resist vehicle roll during a turn.
Anti-roll bars, also known as sway bars, are used in vehicle suspensions for helping to resist vehicle roll during a turn. Anti-roll bars may be used in both the front and rear suspensions of a vehicle.
Anti-roll bars are generally U-shaped and include opposite first and second end portions and an intermediate portion. The first end portion is fixed to the right-hand side of the vehicle suspension and the second end portion is fixed to the left-hand side of the vehicle suspension. During a vehicle turn, the first end portion and the second end portion of the anti-roll bar move relative to one another. As a result, the intermediate portion of the anti-roll bar may be subjected to a torsional force. The torsional stiffness, i.e., the resistance to the torsional force, of the intermediate portion of the anti-roll bar helps to resist vehicle roll during the turn.
The stiffness of the anti-roll bar is also known to increase the spring rate of the vehicle suspension. The independence of the right-hand side and the left-hand side of the vehicle suspension may be affected by connecting the two sides with the anti-roll bar. Consequently, the vehicle ride may be affected, especially when the vehicle is traveling in a linear direction.
Known systems have attached at least one end portion of the anti-roll bar to the vehicle suspension with an actuator. The actuator includes a cylinder and a piston that is movable within the cylinder. The piston divides the cylinder into two variable volume chambers. The known systems further include a source of fluid and a control valve, both of which are independent of the actuator. The control valve is connected to each chamber of the piston by a hydraulic conduit. The control valve has three positions. In a first position, the control valve interconnects the hydraulic conduit connected to each chamber of the actuator, thereby allowing unrestricted movement of the piston in the cylinder. In a second position, the control valve sends hydraulic fluid to the first chamber and receives hydraulic fluid flowing out of the second chamber. In a third position, the control valve sends hydraulic fluid to the second chamber and receives hydraulic fluid flowing out of the first chamber. A system similar to that described above is disclosed in U.S. Pat. No. 5,529,324.
Although the known system helps to reduce the possible effects of the anti-roll bar on the spring rate of the vehicle, the known system includes many parts and installation of the known systems on a vehicle is complex.
This invention is an apparatus for use in a vehicle suspension. The apparatus comprises an anti-roll bar having opposite first and second end portions. An intermediate portion is interposed between the first and second end portions and is subjected to torsional forces when the first and second end portions move relative to one another. The apparatus further comprises an actuator for attaching at least one of the first and second end portions to a part of the vehicle suspension. The actuator comprises a cylinder for retaining fluid and a piston assembly for dividing the cylinder into two chambers. The piston assembly is movable within the cylinder. The piston assembly includes structure forming orifices for interconnecting the two chambers of the cylinder. A fluid flow area of the orifices is adjustable to vary a resistance to relative movement of the first and second end portions of the anti-roll bar.